Once the rocket reaches about 60km the FFU or Free Flying Unit of SQUID must be ejected, starting its active phase. The ejection of the FFU is critical, as any kind of perturbation or missalignement with respect to the rotation axis of the rocket would affect its attitude, which would surely ruin the controlled deployment we are trying to test.

It is also important that the FFU is ejected at the correct speed. If the speed is low it can happen that the rocket caches the FFU and collides with it (it has happened before), and if it is ejected too fast, the FFU can collide with the nosecone (which is obviously ejected before the FFU).

The part in charge of carrying the ejection system and serve as an interface between the rocket and the FFU is called RID. It will bring three different components, the wide angle camera, a wire cutter and springs for the ejection system and an umbilical connector to the FFU, which will be used to “listen” to the experiment while it is on the rocket and the NSSB (Not So Smart Box).

Gustav and Johan Juhlén of LAPLander have been working on our in-house developed stepper motor control circuitry, and now it’s finally running! Right now it’s all prototype boards and code run off a PC with Labview, but everything will be integrated into printed circuit boards and embedded coding.

Since our experiment is very complex and has many tasks to carry out, we thought it was high time to describe its mission and give you an overview of the experiment itself. First, the mission timeline!

It’s in the beginning of March 2011. The Free Flying Unit (FFU) part of the experiment sits right underneath the nose cone of the rocket. It’s shaped like a disc and held firmly in place by a wire against a plate with electrical contacts. Nearby is a forward facing camera, ready to record the ejection from the rocket.

An example of how the FFU may be attached inside the nosecone of the rocket. The airbags and their covers are not shown here

Lift-off! Suddenly everything on the rocket is subjected to 20g of acceleration and is shaken violently, as the fins of the rocket spins it up to 4 rotations a second. Thanks to all the vibration testing our experiment stays in one piece, and after 60 seconds and at an altitude of 60km the nose cone is ejected. Shortly thereafter a small explosive charge cuts the wire holding the FFU in place, and a powerful spring pushes it away from the rocket.

The mission has started. The camera attached to the rocket records the receding FFU while it starts deploying the wire booms. Just before they are fully deployed, the motors lower the deployment rate, and they end up at full length without any swinging. Our calculations were correct! Any swinging in the wire booms would disturb the measurements and it was important that this deployment technique worked.

The FFU floating in space, wire booms extended. The airbags and their covers are not shown in this picture.

The FFU is now far from the rocket, and its built-in sensors have collected data from the deployment so we can recreate it in simulation later. As it’s nearing the thicker parts of the atmosphere it’s time to pull in the wire booms. The motors have to fight the centrifugal force as the experiment still has the spin from the rocket, but the booms are pulled in before the underside of the disc starts heating up from the air pressing against it. Soon the surface temperature is over a hundred degrees Celsius. After the violent reentry the experiment is now falling towards the frosty wilderness of Kiruna. About five kilometers above the snow a cutter cuts the rope holding the airbag covers in place, and soon thereafter the pressure tanks inflate the airbags. Between the four airbags a parachute is stretched, and soon the speed is below 10 meters per second.

The FFU falling with airbags deployed (model from the LAPLander drop test)

Just before impact the FFU uses a small satellite modem to transmit its GPS position, which will allow us to pinpoint its landing site. At landing, the airbags cushion the landing, and directly afterwards the recovery beacon starts transmitting. It’s now up to the recovery crew from Esrange in their helicopters to find and recover our experiment so we can analyze the data!

English: The second phase of the KTH on the Inside competition has been kicked off, and with it, KTHs new outrach portal!

Many of us in SQUID are busy with exams this week and the next, so work on the project is temporarily going a bit slower. We promise to keep you updated with all the happenings though… and some exciting things have been going on the last week! Stay tuned.